Treponema denticola is an anaerobic spirochete associated with periodontal disease. The organism cannot easily be used for many types of standard microbiological experiments because it grows slowly with generation times of 17 hours or more and does not readily form discrete colonies on agar media. In attempting to improve procedures for cultivating the organism, we found that it can grow aerobically in media containing oxidation-reduction buffers. It was found to be catalase negative but to have superoxide dismutase activity, as much as 1.52 units/mg cell protein. The enzyme was released from cells following brief sonication. However, further isolation and purification has proven to be difficult because of the highly proteolytic nature of the organism. The enzyme was isolated from extracts treated with protease inhibitors by means of polyacrylamide gel electrophoresis with detection of activity in the gel by the inhibition of the riboflavin mediated photochemical reduction of nitroblue tetrazolium. The enzyme migrated in non-denaturing gels at about the same rate as the Fe-superoxide dismutase of Escherichia coli and thus has an apparent molecular weight of some 39 kD. These initial results indicate the T. denticola strains ATCC 35405 and ASLM produce superoxide dismutase and at least partly projected against oxidative damage.